The invention relates generally to power-driven conveyors and, more particularly, to modular plastic conveyor belts suitable for following curved paths.
Many conveying applications require conveyor belts to transport articles along curved paths. In low-tension spiral conveyors, for example, a conveyor belt is wrapped helically around a cylindrical drive tower in a compact arrangement for use inside a freezer, on a cooling line, or in a proofer. Conventionally, metal conveyor belts have been used with spiral conveyors. But, as metal belts wear, black specks or worn-off bits of metal fall on the conveyed articles. In many food applications, black specks are not acceptable. In response to the black-speck problem and other food-contamination problems, modular plastic conveyor belts have begun replacing metal belts in food applications. In an ideal situation, a modular plastic belt is a drop-in replacement for a metal belt once the take-up, tensioning, and other sprockets are replaced. But, because metal belts have inherent beam stiffness, they are often supported from below only intermittently across their width, such as at their side edges and middle. This minimal support structure also allows for good air flow, but requires high beam stiffness from edge to edge. Plastic belts with a lot of open area for air flow and for the collapsibility required to negotiate turns, however, do not normally have much beam stiffness. This lack of beam stiffness causes conventional plastic conveyor belts to sag between the spaced apart supports. Another problem with some conventional modular plastic spiral belts with V-shaped links at the inside edge of the belt is that the amount of open area for air flow through the belt tends to decrease toward the inside edge of the belt as it collapses at the drive tower. And some modular plastic spiral belts have large knuckle links at the outside edge of the belt to bear all the belt pull in a turn. But a plastic hinge rod through the large link is subjected to high shear loads at only two points—one on each side of the large knuckle link. These high shear loads can break the hinge rod and cause the belt to come apart. Furthermore, in high-temperature applications, modular plastic conveyor belts can suffer some belt stretch and can, in rare circumstances, burn.
Consequently, there is a need for conveyor belts with increased beam stiffness for wide belt constructions, plenty of open area across its width, better distributed shear in the hinge rods, and heat resistance.